We installed the side rods (sometimes referred to as coupling rods) on the chassis again and rotated the wheels to see where there was some binding. They turned over nearly perfectly, but there was some slight binding in one or two areas that went away once the nuts on the ends which held everything together were tightened up. In the future I should probably put some threadlocker on them to prevent them from working loose while running the locomotive.

The next step was the leading crankpins, which only have the side rods (“coupling rods”) bolted around them. I had machined them slightly longer in the back and as a result they stuck out of the wheel’s rear face. Less than a 1/32, it came off quick in the lathe. Then, the wheel’s crankpin hole was cleaned as was all surfaces of the crank pin. Some Loctite #680 was applied to the shaft of the crank pin and it was inserted and swirled around the hole to distribute the adhesive, and it was left to cure. I inserted a piece of paper behind the axle box and the thrust washer so that if any Loctite oozed out it wouldn’t bind the two together. The other wheel got the same treatment, and the job was done.

I decided to work on the Return Cranks next. Because this is Hackworth valve gear, all of the motion is on the outside and admittedly it doesn’t look as neat as Walschaerts valve gear. But, it is a lot simpler than inside Stephenson valve gear and easily accessible, which is important to me. Because there was going to be a bit of machining involved, I went with hot rolled over cold rolled as I didn’t want to deal with deflection. I laid everything out on some ¼” thick steel I had on hand. However, it had a bow in it from the so it was first passed back and forth on the belt sander to remove the hump in the middle. It was pretty simple layout work, and a circle tracing template came in handy. Drilling out the holes resulted in me losing some 1/16” drill bits in the process. Cheap steel I would imagine. A large belt sander took care of rounding the ends.

Return Crank layout.jpg (15.75 KiB) Viewed 2243 times

The slot was a bit tricky. Jack Buckler’s book instructed not to use a mill to completely make it because it would be too large for a 5” engine. Instead, he suggested milling most of the way through from the back and finishing the slot by using a hacksaw to break through the final 1/32” or so. Instead, I drilled a 5/64” hole at one end of the slot and there was already a 3/8” hole on the other end so we used a hacksaw to carefully connect the two. We later discovered that the slot was too narrow to get a good clamping action, and I used a Dremel tool and a thin file to open it up a bit.

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To provide for the area where the return crank clamps onto the end of the driving crank pin, a small flat spot was milled on one side and then a hole was drilled through #28. The bottom portion of the hole on the lower side of the slot was drilled #36 and then tapped 6-32, which allowed a 6-32 SHCS to be passed through from the top and tightened. The ends of the driving crank pins were discovered to be slightly tapered, so I corrected that. I then used an expanding reamer to open up the 3/8” diameter hole in each of the return cranks to just slip onto the ends of the driving crank pin. Once that was done, we put the return cranks in a vice and tightened them at the slot a little bit. After that, they clamped tightly but it of course will need to be drilled and pinned later on after adjusting the valve gear.

The hole at the other end of the return crank has the return crank pin pass through it, and it was designed to have a “T” shaped crank pin pressed into a recess from the back. We decided to skip the “T” profile and just have it as a straight pin made from some stainless steel stock which will be Loctited in place. While I saw various methods for retaining the cranks and vibrating levers on the pins, most involved drilled a hole through the front (visible) end of the crank pin and then using some sort of bent wire that looked pretty ugly. So, I instead cut slots in the ends of the pin to fit c-clips. A specially ground tool my friend had made cut the slots real quick. I actually cut slots on both ends of the pin, and when it comes time to Loctite them into the return cranks I will push the pin snug against the ring on the rear and later mill it away once the glue cures.

I purchased some cold rolled steel and laid out the parts, using one straight edge from the stock for each side and angling the other one in the middle of the bar. The hole which rotates around the return crank pin has a bronze pushing pressed in and then reamed. One side of the lever was first cut on the band saw and then milled down to the scribed line. There is also a slot that the extension rod connects to, and that slot is supposed to be perpendicular to the vibrating lever.

Vibrating lever layout.jpg (22.33 KiB) Viewed 2242 times

While I think I laid it out perfectly with squares and such, it isn’t critical as long as the slot is wide enough for the full movement of the extension rod without binding. There are probably a lot more scientific ways to clamp the vibrating lever in the mill vice and then machine the slot, but I went with the easy one. I took a piece of wood and drilled two holes along its centerline and then bolted the lever onto the wood. This held the piece perfectly centered in the vice, and milling the recess slot was then easy. Beyond that, it wasn’t a difficult part to make.

Once I put everything together so far (the driving crank pin, return crank, return crank pin, vibrating lever, and the retaining c-clips) I couldn’t help but push the pieces around and around! One thing I have found useful is to search the internet and especially the company Station Road Steam's "Archives" https://www.stationroadsteam.com/archive/ to look at pictures of other Sweet Pea and Sweet William engines. There is a tremendous amount of differences in how each person has built his engine, including such things as fittings and joinery techniques. I sometimes print out pictures of various pieces I am working on and keep them as a reference. That explains the picture of the green engine behind my valve gear parts.

The weighshaft is the rod that runs perpendicular to the frame which holds the slides (or slide boxes) on its ends. These slides connect to the valve gear and the slides are adjusted by linkages connecting to a lever in the cab. Though primitive, by rotating the slides on the end of the weighshaft the amount of admission to the cylinders is controlled and thus even an engine with Hackworth valve gear can be adjusted for efficiency. I don’t know if American locomotive builders called this rotating rod something special, but English builders called it the weighshaft.

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The original plans called for supporting the weighshaft on brackets which bolted to the frame, and it passed through a tube with bearings which were slipped into the ends of the tube and welded on. The tube the weighshaft ran in was free to slide from side to side on its own accord and so as to prevent this it was drilled and pinned to the brackets by inserting bolts down through the thickness of the bracket into the tube. This seems fiddly and not very strong, and I discussed it on the forum here: http://www.chaski.org/homemachinist/vie ... 80#p393380

The reason it was done this way originally was so that the brackets, weighshaft, tube, and slide boxes could all come apart if necessary. Since the publication of the plans originally, the designer suggested tapering the ends of the weighshaft and making the portion that fits between the brackets thicker so that it cannot slide through the brackets. If something happens to the valvegear the weighshaft can rotate around but it is still captive between the brackets. If I ever need to remove it all, I can unscrew the brackets from the frame and lift the assembly out.

I purchased some 1/4" thick steel plate to use for the brackets. Since the edges of the steel were rounded over from the manufacturing process, I laid out the pieces in the middle of the plate and cut them to shape. The mill was used to clean up the large straight edges, and then using measuring triangles the pieces were clamped in the mill again and the angles were cut. They aren’t critical and just add to the looks of the pieces, having less metal and thus less mass. But, they will be highly visible so I wanted to get them right. The rounded portion was taken care of on a large belt sander.

weighshaft rough pieces.jpg (10.23 KiB) Viewed 776 times

The holes for the weighshaft bearings were drilled and then reamed to just under the diameter of some bronze bushings we had on hand, and then they were pressed in. The bearings had a flange on them which extends out from the frame bracket, adding just a slight amount more of support to the weighshaft. The insides of the bushings were reamed again. The brackets were number punched to indicate which side of the frame they went with (sadly, my frames are not perfectly identical) and then I also punched the word “IN” on the inner-facing surface in a spot that isn’t visible when they are attached to the frame.

The frame mounting holes were transferred from the frame, and we did one side at a time. Once the first bracket was drilled and mounted, the other was clamped to the frame and we used a piece of steel rod to make sure the other bracket was exactly in the right position and elevation. Then, the other holes were transferred. I don’t know if this amount of precision is necessary, but the less slop in the valve gear the better.

There are two slides required for my engine, one on each end of the weighshaft. One of them also has a bracket bolted on that connects to rods which run to the cab that are shifted to adjust the cut off for the cylinders. I built mine using the revised, 7.25” gauge plans which called for a base piece with a trench milled all the way through it and a cover which bolted on top that had a clearance slot cut in it. The cover was retained by many screws which have to be countersunk into the cover to provide clearance for the valve linkages that slide up and down just above the cover.

The original plans called for making the slides in three pieces which you can conceptualize if you were lay the slide flat on its back with the slot facing up: one “bottom” piece which the slide block would ride on and two “sides” that bolted onto the bottom piece which came up and over the bottom piece. In other words, it would be two “L” shaped pieces that clamped onto the main piece. This looked clunky but it avoided the problem in the smaller scales of trying to make a separate cover with countersunk screws in something so small. By having the “L” pieces clamp onto the sides (where there are no clearance issues), the distance between the “L” pieces creates the slot and no binding will occur.

Now that the probably useless design lesson is over, I used 1045 for my slides themselves. After cutting two pieces to their rough length, I milled them to the final dimensions all over. Then, using a smaller mill cutter I started working on the trench. In reality, it doesn’t need to run all the way through as the slide block never fully reaches the top or bottom of the slot. However, for ease in machining I did it the entire way. While that means grit and dirt can get in from the top or bottom, I assume that it means that this same debris can more easily be cleaned out too. Had the slot been entirely contained, anything that got in would be stuck in there unless I unbolted the cover and cleaned it out.

slide - milling trough.jpg (28.52 KiB) Viewed 775 times

I was very careful when milling the slots not to cut to the final dimensions until I was ready for a final pass, as I really wanted the slide blocks to be a nice fit. I had the slide blocks already made and I used them as a go/no go indicator for each slide. It was impossible to get perfect 90-degree corners at the bottom of the slots, so we had a slightly knock off the corners of the slide blocks themselves. Finally, though, after several hours (I am a slow machinist) everything fit just perfectly with no slop whatsoever.

slide blocks in trough.jpg (26.47 KiB) Viewed 775 times

The brass slide blocks were made next. Perhaps I should have used bronze but I had the brass on hand. These are such easy pieces to make that if they show too much wear from operation I can always substitute bronze ones at a later date. Each is essentially a rectangle with a small lip on the top of the edge that faces out, which I assume is suppose to be a wall to hold in lubricating oil (which seems like it would be flying all around anyway and not much use). There is a 1/2" diameter stainless steel pin that is inserted in the back of the slide block which sticks out from the slide through the slot on the cover and connects to the valve gear, and this pin has a flange that is recessed into the back of the slide block. So, I drilled through the slide block and then countersunk the hole. The end of the pin was slotted for “e” clips which I prefer using whenever possible.

The covers were made from some 1/8” thick steel which was milled to the correct dimensions. I laid out the 8 mounting holes for each cover and also two 7/16” holes for the top and bottom of the slot that the pin would stick out from. The holes were then drilled and I transferred the hole locations to the slides themselves. Looking back on it now, once the trench was milled in the slide the edges on either end were pretty narrow and the 8 cover mounting screw holes had to be drilled and tapped into them. It wouldn’t have hurt anything to make the slides a little bit wider on the edges which would have left more room for the 8 holes. As it turns out, things worked out well but I can see why doing it in a smaller scale would be frustrating.

slide covers - laying out.jpg (24.05 KiB) Viewed 774 times

The 8 holes in the slides were then drilled and tapped 4-40 using a powertap. I had intentionally drilled the holes longer than the screws we were using, so we had no fear of running the tap into the bottom of the hole by mistake. The holes in the cover were then countersunk and the 16 total mounting screws were screwed in. Actually, in all honestly, only 15 were done because one hole on the cover was drilled slightly off-line and I couldn’t drill and tap the slide for it. If this really bothered me I could have remade one of the covers with all 8 holes properly lined up but I am confident that 7 screws in one slide will be sufficient. The covers were slightly oversize on one edge but a large belt sander took care of that pretty quick.

slides - holes drilled and tapped.jpg (29.46 KiB) Viewed 774 times

Then, I slipped the slide blocks into the slides with the covers still screwed on and the slides ran up and down all the way without any slop or binding. This was a very good feeling. Finally, the very center of the backs of the slides were drilled and then reamed out to 3/8,” which is what the end of the weighshaft was turned down to. As noted above, they will be pinned at a later date during valve gear setting.

Of course, things are never as easy as they sound. During the course of building this engine I have had to remake the brackets which maintain the alignment of the suspension springs that ride above the axle boxes at least three times. That is because the plans as originally drawn put the axle boxes too far outward and they interfered with the inner face of the drive wheels. When we shifted by shimming the axle boxes inward, clearance was restored but the brackets needed to be remade. Along the way I removed the new ones and misplaced them, so I had to remake them again.

I noticed that the plans called for 3/4" angle iron but I used 1" as that is all I could find in the correct thickness. I never bothered to mill it down as I assumed it would be lost in the shadows of the frame and it wouldn't appear too balky. It was only upon installing the weighshaft brackets that I found out the true reason: they interfered with one another. So, the suspension brackets came off again and were milled down, and finally everything fits as it should.

weighshaft suspension interference.jpg (19.14 KiB) Viewed 773 times

The two holes in the brackets will have bolts screwed down from the top, and they will retain suspension springs which will sit over the socket head cap screws located on the tops of the axle boxes.